214 PHYSIOLOGICAL CHEMISTRY 



of chlorides by acidifying and reprecipitating with, nitric acid. 



2. Sulphates. Add dilute hydrochloric acid and barium 

 chloride. Write the equation. The precipitate is barium sul- 

 phate. 



Note: Sulphates are present only in small amounts in 

 most body tissues and fluids. Unless care is exercised, a 

 slight precipitate of sulphates will be overlooked. The 

 sulphate test should be observed carefully in a good light, 

 and compared with the original solution which is being 

 tested in order to detect a possible slight precipitate. 



3. Phosphates. Add 1-2 c.c. cone, nitric acid and about 

 2-3 c.c. ammonium molybdate. Warm carefully until just too 

 hot to be held in the hand, and allow to stand. If phosphates 

 are present, a yellow crystalline precipitate of ammonium phos- 

 pho-molybdate will gradually settle to the bottom of the test 

 tube. The precipitate may not form for some time, but its ap- 

 pearance often may be hastened by rubbing the inside of the 

 test tube gently with a glass rod. If the precipitate is curdy, 

 add more nitric acid and boil until it dissolves, as this is not 

 the phosphate precipitate. 



4. Carbonates. The carbonates present in muscle and blood 

 were decomposed by boiling with acid, carbon dioxide being 

 given off. Also the carbonates in bone were partly destroyed in 

 the preparation of bone ash. To detect carbonates in bone, add 

 2-5 c.c. water to a small amount of ground bone and add a few 

 drops of concentrated nitric acid. Observe the bubbles of C0 2 . 

 If the mouth of the test tube is held to the ear, the effervescence 

 may be plainly heard. 



5. Calcium. To 10 c.c. of the solution add about 2 c.c. 

 ammonium oxalate and allow to stand for 15 minutes. The 

 precipitate is calcium oxalate. The test must be made in acetic 

 acid solution as nitric acid dissolves calcium oxalate. Write the 

 equation. Use for the magnesium test the portion tested for 

 calcium. 



6. Magnesium. Filter off any precipitate of calcium oxalate 

 in the liquid tested for calcium. If the filtrate does not come 



